Old English on, unstressed variant of an "in, on, into," from Proto-Germanic *ana "on" (cf. Dutch aan, German an, Gothic ana "on, upon"), from PIE root *an- "on" (cf. Avestan ana "on," Greek ana "on, upon," Latin an-, Old Church Slavonic na, Lithuanian nuo "down from"). Also used in Old English in many places where we would now use in. From 16c.-18c. (and still in northern England dialect) often reduced to o'. Phrase on to "aware" is from 1877. On time is from 1890.

on

Not canceled; scheduled to happen: The deal's still on/ It's on for tomorrow night(1908+)

Accepted and confirmed as a partner, competitive bettor, etc: He said he bet he could do it, and I told him he was on/ You want to go up there with us? You're on(1812+)

Performing; presenting a talk, appeal, etc, as if one were on stage: She's never relaxed, she's always on/ Better review your points, since you're on next (1793+) prep 1 Paid for by; with the compliments of: This was to be on him (1871+) 2 Taking; using; addicted to: He had her on penicillin/ He was on acid and barbiturates at the time(1936+ Narcotics)

The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D.Copyright (C) 2007 by HarperCollins Publishers.Cite This Source